Enhanced Synthesis of Poly Gamma Glutamic Acid by Increasing the Intracellular Reactive Oxygen Species in the Bacillus licheniformis Δ1-pyrroline-5-carboxylate Dehydrogenase Gene ycgN Deficient Strain

Poly gamma glutamic acid (γ-PGA) is an anionic polyamide with numerous applications. Proline metabolism influences the formation of reactive oxygen species (ROS), and is involved in a wide range of cellular processes. However, the relation between proline metabolism and γ-PGA synthesis has not yet been analyzed. In this study, our results indicated that the deletion of Δ1-pyrroline-5-carboxylate dehydrogenase encoded gene ycgN resulted in 85.22% higher yield of γ-PGA in B. licheniformis WX-02. But the deletion of proline dehydrogenase encoded gene ycgM had no effect on γ-PGA synthesis. Meanwhile, a 2.92-fold higher level of P5C was detected in ycgN deficient strain WXΔycgN, while the P5C levels in WXΔycgM and double mutant strain WXΔycgMN remained the same, compared to WX-02. The ROS level of WXΔycgN was 1.18-fold higher than that of WX-02, and the addition of n-acetylcysteine (antioxidant) into medium could decrease its ROS level, further reduced the γ-PGA yield. Our results showed that proline catabolism played an important role in maintaining ROS homeostasis, and the deletion of ycgN caused P5C accumulation, which induced a transient ROS signal to promote γ-PGA synthesis in B. licheniformis.Importanceγ-PGA is an anionic polyamide with various applications in biomedical and industrial fields. Proline metabolism influences the intracellular reactive oxygen species (ROS) and is involved in a wide range of cellular processes. Here, we report the effects of proline metabolism on γ-PGA synthesis. Our results indicated that deletion of ycgN promoted the synthesis of γ-PGA by increasing the intracellular levels of Δ1-pyrroline-5-carboxylate to generate a transient ROS signal in B. licheniformis WX-02. This study provides the valuable information that enhanced synthesis of γ-PGA by knocking out of ycgN.